An electric arc occurring in a direct current (DC) circuit may be recognized by detecting high-frequency alternating currents (AC) within the DC circuit which are symptomatic for an electric arc.
For the detection of AC currents in a DC circuit, several types of sensors are known. Examples of such sensors are winding type transformers, e.g. so-called Rogowski coils, or shunt resistors, at which a voltage drop may be measured if an AC current occurs. When using such sensors it is usually necessary to modify the construction of the DC circuit. For example, when using a winding type transformer, a DC conductor has to be fed through the winding type transformer, or when using a shunt resistor, it has to be placed within the DC circuit appropriately and additionally causes an increase of power losses within the DC circuit.
DC circuits may be sensitive to external electromagnetic fields or may be connected to devices which generate AC current components, e.g. power converters comprising high-frequency switching devices, and may even generate and emit electromagnetic fields themselves. In order to comply with electromagnetic compatibility (EMC) regulations, such DC circuits often comprise filters which suppress unwanted AC content from the currents flowing within the DC circuit in order to attenuate electromagnetic radiation emitted by the DC circuit. In particular, a common mode choke is often used to suppress AC currents flowing in the same direction through the positive and negative conductors of the DC circuits, i.e. so-called common mode currents. Such a common mode choke comprises at least two partial windings which are wound on a common core and which are connected to the positive and the negative conductors of the DC circuit, respectively. Such a common mode choke has a high inductance for common mode currents, i.e. for AC currents flowing in the same direction through conductors of the DC circuits which are arranged substantially parallel and in which a DC current flows in opposite directions. On the other hand, a common mode choke has a very low inductance for differential mode currents, i.e. currents flowing in opposite directions through the conductors of the DC circuit, hence the common mode choke has a negligible effect on the DC current and differential mode AC currents flowing parallel or antiparallel to the DC currents.